Plastic pipes have been widely used in many fields due to good corrosion resistance, light weight and convenience of installation. However, applications in the industrial field are limited because of lower mechanical strength, lower rigidity and decreased heat-resistance over standard metal pipes. There are numerous configurations of pipe and methods of manufacturing same found in the prior art that have been designed to provide increased mechanical strength, increased rigidity, and greater heat-resistance over plastic pipes.
One example is described in U.S. Pat. No. 3,242,691 to Robinson et al., which describes a method of producing a pipe that includes a flexible shaft assembly including a flexible rotatable metal core, an inner plastic tubing sized to receive the metal core, a plurality of metallic wires helically wound in one direction, and a second plurality of metallic wires helically wound in the opposite direction.
Another example is described in U.S. Pat. No. 3,460,578 to Schmid, which describes a composite flexible shaft casing including an inner plastic liner, a wire braid having wires helically wound to form interstices between the wires, an outer covering extruded over the wire braid and passing through the interstices to engage the liner, and a plurality of axially extending ribs or projections.
U.S. Pat. No. 3,526,692 to Onaka describes a mechanism for continuously coiling wire into a helix and feeding the helix axially through a plastic extruding die where a plastic pipe body is extruded so that the wire helix is embedded in but projects from the outer surface of the pipe body. The pipe body is then passed through a second plastic extruding die in which a tubular plastic layer is bonded to the outer surface of the pipe body.
U.S. Pat. No. 4,258,755 to Higbee describes a flexible reinforced cured resin hose including a combination of helically wound cable wires and body wires embedded therein. Two plies of wires are wrapped in opposite directions around the periphery of a liner tube supported on a mandrel, the plies being supported in a resin filler layer applied over the liner to hold the wires spaced apart.
Yet another example is found in U.S. Pat. No. 4,657,049 to Fourty et al., which describes a reinforced composite tubular body including a metallic reinforcement of helical convolutions completely embedded in a tubular body of thermosetting polymer which has a coefficient of elongation at rupture less than 15%.
Another example of a steel skeleton-plastic composite pipe is described in China Patent 94104509. The pipe described in China Patent 94104509 has distinct advantages over plastic pipes and over other steel-plastic composite pipes known to those skilled in the art, including increased mechanical strength, increased rigidity, and a greater heat resistance. The steel skeleton according to that patent is constructed by both longitudinal and traverse reinforcing wires, and the amount of both longitudinal reinforcing wires and traverse reinforcing wires in the steel skeleton are 50% respectively. To increase the strength of the pipe, the diameter of the transverse reinforcing wire is increased. This results in increasing the wall thickness of the composite pipe.
The devices and methods described in the prior art achieve a certain degree of success in increasing mechanical strength, increasing rigidity, and providing greater heat tolerance in pipe. However, it would be desirable to increase the mechanical strength of a component pipe without significantly increasing the wall thickness. It would also be desirable to provide a method of manufacture of not only composite straight pipe, but also composite pipe components, wherein the method of manufacture offers significant savings in the cost of manufacture.